The photographer John Thompson (1837-1921) used the Woodburytype process patented in 1864 for the images in Street Life in London, including this photograph. Woodburytype was a photomechanical method of reproduction involving a sheet of light-sensitized pigmented gelatine, usually of a rich purple-brown colour, exposed to light through a negative. The gelatine hardens in proportion to the amount of light to which it is exposed and when soaked in warm water the unhardened gelatine is washed away. This was the first mechanical process that could successfully reproduce a photograph. The resultant image is in slight relief when seen through a magnifier. The process was complicated but remained popular until about 1900 because of the high quality and permanence of the finished images.